Surfactants electrolyte addition

Zhong et al. (2003) studied the apparent solubility of trichloroethylene in aqueous solutions, where the experimental variables were surfactant type and cosolvent concentration. The surfactants used in the experiment were sodium dihexyl sulfo-succinte (MA-80), sodium dodecyl sulfate (SDS), polyoxyethylene 20 (POE 20), sorbitan monooleate (Tween 80), and a mixture of Surfonic- PE2597 and Witconol-NPIOO. Isopropanol was used as the alcohol cosolvent. Eigure 8.20 shows the results of a batch experiment studying the effects of type and concentration of surfactant on solubilization of trichloroethylene in aqueous solutions. A correlation between surfactant chain length and solubilization rate may explain this behavior. However, the solubilization rate constants decrease with surfactant concentration. Addition of the cosolvent isopropanol to MA-80 increased the solubility of isopropanol at each surfactant concentration but did not demonstrate any particular trend in solubilization rate of isopropanol for the other surfactants tested. In the case of anionic surfactants (MA-80 and SDS), the solubility and solubilization rate increase with increasing electrolyte concentration for all surfactant concentrations. 

An increase in the phenanthrene partition coefficient for SDS micelles is observed with increasing ionic strength at a fixed pH of 6 (Table 2). A conceptual model has been proposed to describe the effects of electrolyte addition on the partitioning of nonpolar compounds such as phenanthrene into the core (or deep region within the palisade layer) of ionic surfactant... 

CMCs in the absence of added electrolyte may be greatly influenced by electrovis-cous effects marked decreases in intrinsic viscosity on electrolyte addition have been observed in many cases36). Peculiar and highly interesting rheological properties of surfactant solutions include observations of strongly non-Newtonian behavior as well as of viscoelasticity these are yet incompletely understood. 

The results obtained for PTFE latices show clearly that the surface charge of the latex particle plays an important role in determining its stability to electrolyte addition and also that the stability can be affected by the presence of surfactant. 

The effect of electrolyte addition to oscillatory behaviour has also been considered in [235]. The disappearance of structural transition upon electrolyte addition was attributed to its electrostatic origin. The viscosity of the film did not differ much from that of the bulk solution in the case when micelles determined the structuring of the amphiphile surfactant molecules. It is worth to note that the length scale of the oscillations was large, about 10 nm and even reached about 50 nm. 

The quantity xp is a much better defined characteristic of foam stability (since the pressure in the borders along the height of the foam column remains constant during its destruction). This parameter is also much more sensitive to the kind of surfactant, electrolyte concentration and other additives, compared to the lifetime of the foam in gravitational field, with an averaged pressure value from 0 to pgH. Estimation of the stability of foams from different surfactants by xp and by the Ross-Miles test has been reported in [16]. The results are discusses in Section 7.6.1. The advantages of the Foam Pressure Drop Technique and, respectively, xp as a characteristic of the foam stability, are clearly shown. 

These metal/F2-treated PTFE composite films, with metals such as Ni, Au, Sn, Cr can also be prepared by electrodeposition in an electrolyte solution in which PTFE micrometric particles are suspended by using a cationic surfactant. In addition to their very high contact angle (130 < 0(°) < 155), the films show good corrosion... 

We have examined the stmcture of both ionic and nonionic micelles and some of the factors that affect their size and critical micelle concentration. An increase in hydrophobic chain length causes a decrease in the cmc and increase of size of ionic and nonionic micelles an increase of polyoxyethylene chain length has the opposite effect on these properties in nonionic micelles. About 70-80% of the counterions of an ionic surfactant are bound to the micelle and the nature of the counterion can influence the properties of these micelles. Electrolyte addition to micellar solutions of ionic surfactants reduces the cmc and increases the micellar size, sometimes causing a change of shape from spherical to ellipsoidal. Solutions of some nonionic surfactants become cloudy on heating and separate reversibly into two phases at the cloud point. 

The addition of agents with charges opposite to those of the film these can include surfactants, electrolytes or iodized drugs with the opposite charge. 

The overall characteristics of the finished product are the result of the presence of the additives (nonionic surfactants, electrolytes, cationic polymers), of the nature and amount of the perfume, and of the manufacturing procedure (temperature, stirring) [5],... 

The addition of neutral electrolyte to solutions of nonionic POE surfactants increases the extent of solubilization of hydrocarbons at a given temperature in those cases where electrolyte addition causes an increase in the aggregation number of the micelles. The order of increase in solubilization appears to be the same as that for depression of the cloud point (Section IIIB, below) (Saito, 1967) K+ > Na+ > Li+ Ca2+ > Al3+ SO4 > Cl-. The effect of electrolyte addition on the solubilization of polar materials is not clear. 

Ionic surfactants with only one alkyl chain are generally extremely hydrophilic so that strongly curved and thus almost empty micelles are formed in ternary water-oil-ionic surfactant mixtures. The addition of an electrolyte to these mixtures results in a decrease of the mean curvature of the amphiphilic film. However, this electrolyte addition does not suffice to drive the system through the phase inversion. Thus, a rather hydrophobic cosurfactant has to be added to invert the structure from oil-in-water to water-in-oil [7, 66]. In order to study these complex quinary mixtures of water/electrolyte (brine)-oil-ionic surfactant-non-ionic co-surfactant, brine is considered as one component. As was the case for the quaternary sugar surfactant microemulsions (see Fig. 1.9(a)) the phase behaviour of the pseudo-quaternary ionic system can now be represented in a phase tetrahedron if one keeps temperature and pressure constant. 

Cationic surfactants are separated using direct UV detection or indirect UV detection with a chromophore as electrolyte additive. The addition of organic solvents as modifiers to the electrolytes is essential to obtain efficient separations because of the ability of cationic surfactants to adsorb onto the capillary surface. 

When the macromonomer is used as surfactant (even if it does not display actual surfactant properties) the latex obtained shows an excellent resistance to flocculation due to electrolyte addition (barium chloride) up to the highest concentration examined (0.75 mol/dm ), while conventionally charged latex flocculated at 2.1 x 10" mol/dm. In addition, highly ordered packing of the... 

Some hydrophobic cations, such as tetrabutyl ammonium, appear to have the opposite action on the CMC. OH acts as normal anion whereas practically has no effect up to ca 0.5 M and it rise the CMC at higher concentrations in view of the ether oxygen protonation of the ethylene oxide chain. As a result of electrolyte addition, strong specific binding of ions may make surfactants sometimes more soluble and, in contrast, it may cause coacervation. Surfactant precipitation or strong aggregation occurs in many cases. 

The study of electrolyte effects on the surfactant behaviour in aqueous solutions has shown that even for industrial surfactants which are mixtures of homologues the electrolyte effect on c and CMC is significant. At a sodium chloride concentration of 100 g/1 the CMC of sodium alkyl sulphates decreases by more than one order of magnitude. Relatively small electrolyte additives (up to 10 g/1) increase the stability of foams, i.e. an increase of Wp° is observed at lower bulk surfactant concentrations. However, a subsequent increase in electrolyte concentration produces practically no influence on Wp . As noted above, an appreciable volume of bubble foam is produced not only at Wp = 0, but also in the entire interval 0 < Wp <100. Throughout the whole concentration range, the addition of electrolyte lowers the Wp value by 20—30 %. For example, while there is practically no foaming (Wp = 95 %) at 0.0045 wt% of Cio—Ci3 sodium alkylsulphates in distilled water, the Wp value falls to 60 % with the addition of sodium chloride up to the concentration of 10 g/1 and the formation of an appreciable amount of foam is observed in the experiment. 

---